Conventionally, injection control of fuel to be supplied to an internal combustion engine, and ignition control at each cylinder of the engine are performed based on the intake air amount and other parameters by an electronic control unit (control device). The control device obtains the intake air amount based on a signal transmitted from a flow measuring device provided separately from the control device (see, e.g., JPH06-308142A).
The flow measuring device is disposed in a flow passage for intake air (hereinafter referred to as an air intake duct), and produces a signal in accordance with the intake air amount in the air intake duct (hereinafter referred to as a flow rate signal) by a flow sensor. The flow measuring device transmits the generated flow rate signal to the control device. The control device obtains the intake air amount based on the flow rate signal received from the flow measuring device, and calculates fuel injection timing, a fuel injection period, ignition timing, and so forth using the obtained intake air amount to perform the injection and ignition of fuel.
The transmission of the flow rate signal from the flow measuring device to the control device is performed by wire communication using a harness. For this reason, noise generated in devices around the harness may be superimposed on the flow rate signal. Based on the flow rate signal on which the noise is superimposed, the control device may obtain the intake air amount as an incorrect numerical value.
Accordingly, such a configuration that noise is not easily superimposed on the flow rate signal is required for a communication system between the flow measuring device and the control device. In a vehicle in recent years, the number of noise generating sources tends to increase in line with progress of electronic control of devices disposed therein. From this point of view as well, there is a higher possibility that the noise is superimposed on the flow rate signal, and there is a strong demand for restraint of the noise superimposition.
According to JP2013-036892A, there is also disclosed a configuration of a flow measuring device that generates a signal (temperature signal, humidity signal, or pressure signal) in accordance with, for example, temperature, humidity, pressure of intake air in addition to the intake air amount and transmits the signal to a control device. When the number of signals to be transmitted increases as described above, the number of terminals and harnesses for transmission to the control device also increases to cause a cost increase.